On Friday, January 11, 2019 at 8:53:41 PM UTC-5, George Herold wrote:> On Friday, January 11, 2019 at 3:05:14 PM UTC-5, dagmarg...@yahoo.com wrote: > > On Friday, January 11, 2019 at 12:44:48 AM UTC-5, Phil Hobbs wrote: > > > On 1/10/19 11:46 PM, dagmargoodboat@yahoo.com wrote: > > > > RF MOSFETs. They're built for linear operation. At a glance, they seem > > > > > > Welcome back! You've been a bit scarce since last spring, iirc. > > > > > > Cheers > > > > > > Phil Hobbs > > > > Hi Phil! > > > > I've been doing some pretty fun things, but hobby-level > > electronics, nothing I thought would be very interesting > > for sed. I do still peek in to see what's happening. > James!, As a tadpole here on SED I'd love to hear/see any > of your hobby level 'fun' stuff. > The fare has been a little thin here. > > I'm doing this high side switch driving a heater to ground. > Looking at the circuit I got to work, I've got low pass filters > everywhere, with little understanding... which happens sometimes > when you're just trying to get something working. > > I think my circuit was missing some resistance on the inverting input. > (I tried to do some asci art, but too much of a Friday night buzz. :^) > > High side GS resistor (on pfet) that is turned off by > level sift 'grounded' base npn, with emitter resistor > driven by opamp. A resistor divider senses drain/load > voltage-compares that to error (in opamp) which drives > emitter R. > > George H.Like this? Q1 V+ >--+-----+-. .-------+--------. | | ^ | | | .-. .- - - | | Rgs | | | .-. | '-' | | | Rload | | | '-' | '----+ | | | | | |/ === | +5v >--| Q2 | |>. .-. | | | R1 .-. '-' Re | | /| | '-' /+|-----------+ | / | | '-----< | .-. \ | | | R2 \-|-- Vref '-' \| | === That looks like an oscillator. :-) Cheers, James Arthur
Linear power FETs
Started by ●January 10, 2019
Reply by ●January 12, 20192019-01-12
Reply by ●January 12, 20192019-01-12
<dagmargoodboat@yahoo.com> wrote in message news:f043f83b-114b-43bd-962f-267e9638fb41@googlegroups.com...> You didn't read the OP, did you? > > That's okay, we all put our foot in it sometimes. :-)What, the 350V one? The 200V ones have been around a while; I guess they expect you to cascode for more. You never did say what voltage you're targetting. Don't put your foot in too deep either :-) Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
Reply by ●January 12, 20192019-01-12
On Saturday, January 12, 2019 at 12:58:21 AM UTC-5, dagmarg...@yahoo.com wrote:> On Friday, January 11, 2019 at 8:53:41 PM UTC-5, George Herold wrote: > > On Friday, January 11, 2019 at 3:05:14 PM UTC-5, dagmarg...@yahoo.com wrote: > > > On Friday, January 11, 2019 at 12:44:48 AM UTC-5, Phil Hobbs wrote: > > > > On 1/10/19 11:46 PM, dagmargoodboat@yahoo.com wrote: > > > > > RF MOSFETs. They're built for linear operation. At a glance, they seem > > > > > > > > Welcome back! You've been a bit scarce since last spring, iirc. > > > > > > > > Cheers > > > > > > > > Phil Hobbs > > > > > > Hi Phil! > > > > > > I've been doing some pretty fun things, but hobby-level > > > electronics, nothing I thought would be very interesting > > > for sed. I do still peek in to see what's happening. > > James!, As a tadpole here on SED I'd love to hear/see any > > of your hobby level 'fun' stuff. > > The fare has been a little thin here. > > > > I'm doing this high side switch driving a heater to ground. > > Looking at the circuit I got to work, I've got low pass filters > > everywhere, with little understanding... which happens sometimes > > when you're just trying to get something working. > > > > I think my circuit was missing some resistance on the inverting input. > > (I tried to do some asci art, but too much of a Friday night buzz. :^) > > > > High side GS resistor (on pfet) that is turned off by > > level sift 'grounded' base npn, with emitter resistor > > driven by opamp. A resistor divider senses drain/load > > voltage-compares that to error (in opamp) which drives > > emitter R. > > > > George H. > > Like this? > > Q1 > V+ >--+-----+-. .-------+--------. > | | ^ | | | > .-. .- - - | | > Rgs | | | .-. | > '-' | | | Rload | > | | '-' | > '----+ | | > | | | > |/ === | > +5v >--| Q2 | > |>. .-. > | | | R1 > .-. '-' > Re | | /| | > '-' /+|-----------+ > | / | | > '-----< | .-. > \ | | | R2 > \-|-- Vref '-' > \| | > === > > That looks like an oscillator. :-) > > Cheers, > James ArthurPrezactly! I killed the oscillation with a nF across R2(10k) and 100 nF! of feedback C.> Q1 > V+ >--+-----+-. .-------+--------. > | | ^ | | | > .-. .- - - | | > Rgs | | | .-. | > '-' | | | Rload | > | | '-' | > '----+ | | > | | | > |/ === | > +5v >--| Q2 | > |>. .-. > | | | R1 > .-. '-' > Re | | /| | > '-' /+|-----------+-------. > | / | | | > +-----< | .-. ___ > | \ | | | R2 ___ C2 1nF > | \-|--+- Vrf '-' | > | \| | | ==== > .--C1 0.1uF--. === >Is there some better way to compensate? It's a heater thing so slow is fine. Thanks for the nice pic, I certainly miss your presence. George H.
Reply by ●January 12, 20192019-01-12
On Fri, 11 Jan 2019 21:58:18 -0800 (PST), dagmargoodboat@yahoo.com wrote:>On Friday, January 11, 2019 at 8:53:41 PM UTC-5, George Herold wrote: >> On Friday, January 11, 2019 at 3:05:14 PM UTC-5, dagmarg...@yahoo.com wrote: >> > On Friday, January 11, 2019 at 12:44:48 AM UTC-5, Phil Hobbs wrote: >> > > On 1/10/19 11:46 PM, dagmargoodboat@yahoo.com wrote: >> > > > RF MOSFETs. They're built for linear operation. At a glance, they seem >> > > >> > > Welcome back! You've been a bit scarce since last spring, iirc. >> > > >> > > Cheers >> > > >> > > Phil Hobbs >> > >> > Hi Phil! >> > >> > I've been doing some pretty fun things, but hobby-level >> > electronics, nothing I thought would be very interesting >> > for sed. I do still peek in to see what's happening. >> James!, As a tadpole here on SED I'd love to hear/see any >> of your hobby level 'fun' stuff. >> The fare has been a little thin here. >> >> I'm doing this high side switch driving a heater to ground. >> Looking at the circuit I got to work, I've got low pass filters >> everywhere, with little understanding... which happens sometimes >> when you're just trying to get something working. >> >> I think my circuit was missing some resistance on the inverting input. >> (I tried to do some asci art, but too much of a Friday night buzz. :^) >> >> High side GS resistor (on pfet) that is turned off by >> level sift 'grounded' base npn, with emitter resistor >> driven by opamp. A resistor divider senses drain/load >> voltage-compares that to error (in opamp) which drives >> emitter R. >> >> George H. > >Like this? > > Q1 > V+ >--+-----+-. .-------+--------. > | | ^ | | | > .-. .- - - | | > Rgs | | | .-. | > '-' | | | Rload | > | | '-' | > '----+ | | > | | | > |/ === | > +5v >--| Q2 | > |>. .-. > | | | R1 > .-. '-' > Re | | /| | > '-' /+|-----------+ > | / | | > '-----< | .-. > \ | | | R2 > \-|-- Vref '-' > \| | > === > >That looks like an oscillator. :-) > >Cheers, >James ArthurIs that a linear voltage regulator? There was mention of a highside switch. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●January 12, 20192019-01-12
dagmargoodboat@yahoo.com wrote...> > Winfield Hill wrote: >> dagmargoodboat@yahoo.com wrote... >> > >> > This 650V part puts an enhancement-mode GaN FET in cascode with a >> > depletion-mode GaN JFET. It's real, and it's kind of interesting too: >> > https://www.transphormusa.com/en/document/650v-cascode-gan-fet-tph3206psb/ >> >> LMG3410R070, 600V 40A GaN, 100V/ns, integrated driver and protection. > > I have to make accurate fast rectangular pulses with flat tops > and high edge timing accuracy, so for now I'm wary of having > that much complexity between my trigger and the output signal.There's very little in the signal path. And the 20ns delay to *the MOSFET output* is about as fast as you'll find. My only complaint is that the FETs are too big, too much capacitance. When switching a 50-ohm cable-matching output resistor, a low 70-milli-ohm Ron is serious overkill. -- Thanks, - Win
Reply by ●January 12, 20192019-01-12
On Saturday, January 12, 2019 at 11:00:55 AM UTC-5, George Herold wrote:> On Saturday, January 12, 2019 at 12:58:21 AM UTC-5, dagmarg...@yahoo.com wrote: > > On Friday, January 11, 2019 at 8:53:41 PM UTC-5, George Herold wrote: > > > On Friday, January 11, 2019 at 3:05:14 PM UTC-5, dagmarg...@yahoo.com wrote: > > > > On Friday, January 11, 2019 at 12:44:48 AM UTC-5, Phil Hobbs wrote: > > > > > On 1/10/19 11:46 PM, dagmargoodboat@yahoo.com wrote: > > > > > > RF MOSFETs. They're built for linear operation. At a glance, they seem > > > > > > > > > > Welcome back! You've been a bit scarce since last spring, iirc. > > > > > > > > > > Cheers > > > > > > > > > > Phil Hobbs > > > > > > > > Hi Phil! > > > > > > > > I've been doing some pretty fun things, but hobby-level > > > > electronics, nothing I thought would be very interesting > > > > for sed. I do still peek in to see what's happening. > > > James!, As a tadpole here on SED I'd love to hear/see any > > > of your hobby level 'fun' stuff. > > > The fare has been a little thin here. > > > > > > I'm doing this high side switch driving a heater to ground. > > > Looking at the circuit I got to work, I've got low pass filters > > > everywhere, with little understanding... which happens sometimes > > > when you're just trying to get something working. > > > > > > I think my circuit was missing some resistance on the inverting input. > > > (I tried to do some asci art, but too much of a Friday night buzz. :^) > > > > > > High side GS resistor (on pfet) that is turned off by > > > level sift 'grounded' base npn, with emitter resistor > > > driven by opamp. A resistor divider senses drain/load > > > voltage-compares that to error (in opamp) which drives > > > emitter R. > > > > > > George H. > > > > Like this? > > > > Q1 > > V+ >--+-----+-. .-------+--------. > > | | ^ | | | > > .-. .- - - | | > > Rgs | | | .-. | > > '-' | | | Rload | > > | | '-' | > > '----+ | | > > | | | > > |/ === | > > +5v >--| Q2 | > > |>. .-. > > | | | R1 > > .-. '-' > > Re | | /| | > > '-' /+|-----------+ > > | / | | > > '-----< | .-. > > \ | | | R2 > > \-|-- Vref '-' > > \| | > > === > > > > That looks like an oscillator. :-) > > > > Cheers, > > James Arthur > > Prezactly! I killed the oscillation with a nF across R2(10k) and > 100 nF! of feedback C. > > Q1 > > V+ >--+-----+-. .-------+---------------. > > | | ^ | | | > > .-. .- - - | | > > Rgs | | | .-. | > > '-' | | | Rload | > > | | '-' | > > '----+ | | > > | | | > > |/ === | > > +5v >--| Q2 | > > |>. .-. > > | | | R1 > > .-. '-' > > Re | | /| | > > '-' /+|------------------+-------. > > | / | | | > > +-----< | .-. ___ > > | \ | Rcomp | | R2 ___ C2 1nF > > | \-|--+-/\/\/-- Vrf '-' | > > | \| | | ==== > > '-----||-----' === > > 100nF > > Is there some better way to compensate? > It's a heater thing so slow is fine. > > Thanks for the nice pic, I certainly miss your presence. > > George H.C2 across R2 is anti-helpful. The problem, in lay terms, is that your op-amp is reacting very quickly, but to old news. That is, it's over-reacting to feedback that is delayed in time. So you're creating a situation where you are already driving Q2 appropriately, but Q1's output hasn't moved yet, and your op-amp then tries to drive Q2 even harder even though its existing drive level was already perfect (if it had only waited long enough to see). C2 makes that worse. The easy solution is to eliminate C2 and add in Rcomp. Rcomp, sufficiently large, slows the op-amp response until the feedback delay is inconsequential in comparison to the op-amp's now-gradual corrections. In that way, the op-amp is reacting to a realistic representation of the results of that op-amp's last output, and can make appropriate new adjustments. Another way is to accelerate the feedback to the op-amp so that the op-amp's information isn't so stale, such as with feed-forward compensation. Here, that would mean putting C2 across R1. But if you don't need the maximum speed possible, just slow down the op-amp. It's less ticklish. Slowed down, the op-amp will make corrections gradually, then have plenty of time to see the effects of those corrections, then make even more corrections. Tada! that's also known as 'closed-loop feedback'. :-) Did that make sense? Cheers, James Arthur
Reply by ●January 12, 20192019-01-12
On Saturday, January 12, 2019 at 12:37:54 PM UTC-5, Winfield Hill wrote:> dagmargoodboat@yahoo.com wrote... > > > > Winfield Hill wrote: > >> dagmargoodboat@yahoo.com wrote... > >> > > >> > This 650V part puts an enhancement-mode GaN FET in cascode with a > >> > depletion-mode GaN JFET. It's real, and it's kind of interesting too: > >> > https://www.transphormusa.com/en/document/650v-cascode-gan-fet-tph3206psb/ > >> > >> LMG3410R070, 600V 40A GaN, 100V/ns, integrated driver and protection. > > > > I have to make accurate fast rectangular pulses with flat tops > > and high edge timing accuracy, so for now I'm wary of having > > that much complexity between my trigger and the output signal. > > There's very little in the signal path. And the 20ns delay to > *the MOSFET output* is about as fast as you'll find. My only > complaint is that the FETs are too big, too much capacitance. > When switching a 50-ohm cable-matching output resistor, a low > 70-milli-ohm Ron is serious overkill. > > > -- > Thanks, > - WinWhen you take tpd as of the driver+FET, 20nS isn't bad. But I need sub-nS edge-timing accuracy, so 20nS and a resistor-set slew rate are rather scary to me at a time when I'm worried about logic threshold drift affecting my timings. I think I can manage about half that delay using hand-picked parts, without getting too fancy, and then having the whole signal path available and under my control. Also, mine is a totem-pole driver. I'd have to float the high-side LMG3410, pass its logic commands through an isolator that can handle insane slew rates, and power it all with a floating supply. With the signal isolator, my delay would be approaching 30nS. I'd have to use a similar isolator on the low side to match the high-side delays. All of that is do-able, naturally. But I'm trying to avoid it, here. And I don't trust most of the digital isolators when it comes to jitter--who knows how much those modulated transmission schemes jitter? Excess jitter is something this application can't abide. I do love the LMG3410 though--it is a very tempting concept, and a tempting part. Cheers, James Arthur
Reply by ●January 12, 20192019-01-12
On Saturday, January 12, 2019 at 11:57:16 AM UTC-5, John Larkin wrote:> On Fri, 11 Jan 2019 21:58:18 -0800 (PST), dagmargoodboat@yahoo.com > wrote: > > >On Friday, January 11, 2019 at 8:53:41 PM UTC-5, George Herold wrote: > >> On Friday, January 11, 2019 at 3:05:14 PM UTC-5, dagmarg...@yahoo.com wrote: > >> > On Friday, January 11, 2019 at 12:44:48 AM UTC-5, Phil Hobbs wrote: > >> > > On 1/10/19 11:46 PM, dagmargoodboat@yahoo.com wrote: > >> > > > RF MOSFETs. They're built for linear operation. At a glance, they seem > >> > > > >> > > Welcome back! You've been a bit scarce since last spring, iirc. > >> > > > >> > > Cheers > >> > > > >> > > Phil Hobbs > >> > > >> > Hi Phil! > >> > > >> > I've been doing some pretty fun things, but hobby-level > >> > electronics, nothing I thought would be very interesting > >> > for sed. I do still peek in to see what's happening. > >> James!, As a tadpole here on SED I'd love to hear/see any > >> of your hobby level 'fun' stuff. > >> The fare has been a little thin here. > >> > >> I'm doing this high side switch driving a heater to ground. > >> Looking at the circuit I got to work, I've got low pass filters > >> everywhere, with little understanding... which happens sometimes > >> when you're just trying to get something working. > >> > >> I think my circuit was missing some resistance on the inverting input. > >> (I tried to do some asci art, but too much of a Friday night buzz. :^) > >> > >> High side GS resistor (on pfet) that is turned off by > >> level sift 'grounded' base npn, with emitter resistor > >> driven by opamp. A resistor divider senses drain/load > >> voltage-compares that to error (in opamp) which drives > >> emitter R. > >> > >> George H. > > > >Like this? > > > > Q1 > > V+ >--+-----+-. .-------+--------. > > | | ^ | | | > > .-. .- - - | | > > Rgs | | | .-. | > > '-' | | | Rload | > > | | '-' | > > '----+ | | > > | | | > > |/ === | > > +5v >--| Q2 | > > |>. .-. > > | | | R1 > > .-. '-' > > Re | | /| | > > '-' /+|-----------+ > > | / | | > > '-----< | .-. > > \ | | | R2 > > \-|-- Vref '-' > > \| | > > === > > > >That looks like an oscillator. :-) > > > >Cheers, > >James Arthur > > Is that a linear voltage regulator? There was mention of a highside > switch.I took it as a linear system but you're right, George said "switch." If he literally meant hard-switching Q1, that's a different kettle of fish. A PWM scheme with a slow feedback loop might make more sense for that. Cheers, James
Reply by ●January 12, 20192019-01-12
On Sat, 12 Jan 2019 10:17:47 -0800 (PST), dagmargoodboat@yahoo.com wrote:>On Saturday, January 12, 2019 at 11:57:16 AM UTC-5, John Larkin wrote: >> On Fri, 11 Jan 2019 21:58:18 -0800 (PST), dagmargoodboat@yahoo.com >> wrote: >> >> >On Friday, January 11, 2019 at 8:53:41 PM UTC-5, George Herold wrote: >> >> On Friday, January 11, 2019 at 3:05:14 PM UTC-5, dagmarg...@yahoo.com wrote: >> >> > On Friday, January 11, 2019 at 12:44:48 AM UTC-5, Phil Hobbs wrote: >> >> > > On 1/10/19 11:46 PM, dagmargoodboat@yahoo.com wrote: >> >> > > > RF MOSFETs. They're built for linear operation. At a glance, they seem >> >> > > >> >> > > Welcome back! You've been a bit scarce since last spring, iirc. >> >> > > >> >> > > Cheers >> >> > > >> >> > > Phil Hobbs >> >> > >> >> > Hi Phil! >> >> > >> >> > I've been doing some pretty fun things, but hobby-level >> >> > electronics, nothing I thought would be very interesting >> >> > for sed. I do still peek in to see what's happening. >> >> James!, As a tadpole here on SED I'd love to hear/see any >> >> of your hobby level 'fun' stuff. >> >> The fare has been a little thin here. >> >> >> >> I'm doing this high side switch driving a heater to ground. >> >> Looking at the circuit I got to work, I've got low pass filters >> >> everywhere, with little understanding... which happens sometimes >> >> when you're just trying to get something working. >> >> >> >> I think my circuit was missing some resistance on the inverting input. >> >> (I tried to do some asci art, but too much of a Friday night buzz. :^) >> >> >> >> High side GS resistor (on pfet) that is turned off by >> >> level sift 'grounded' base npn, with emitter resistor >> >> driven by opamp. A resistor divider senses drain/load >> >> voltage-compares that to error (in opamp) which drives >> >> emitter R. >> >> >> >> George H. >> > >> >Like this? >> > >> > Q1 >> > V+ >--+-----+-. .-------+--------. >> > | | ^ | | | >> > .-. .- - - | | >> > Rgs | | | .-. | >> > '-' | | | Rload | >> > | | '-' | >> > '----+ | | >> > | | | >> > |/ === | >> > +5v >--| Q2 | >> > |>. .-. >> > | | | R1 >> > .-. '-' >> > Re | | /| | >> > '-' /+|-----------+ >> > | / | | >> > '-----< | .-. >> > \ | | | R2 >> > \-|-- Vref '-' >> > \| | >> > === >> > >> >That looks like an oscillator. :-) >> > >> >Cheers, >> >James Arthur >> >> Is that a linear voltage regulator? There was mention of a highside >> switch. > >I took it as a linear system but you're right, George said "switch." > >If he literally meant hard-switching Q1, that's a different kettle >of fish. A PWM scheme with a slow feedback loop might make more >sense for that. > >Cheers, >JamesDriving heaters from linear amps is messy. There's the square-law linearity issue, and general inefficiency. PWM is better for heater control. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●January 12, 20192019-01-12
On Saturday, January 12, 2019 at 12:37:54 PM UTC-5, Winfield Hill wrote:> dagmargoodboat@yahoo.com wrote... > > > > Winfield Hill wrote: > >> dagmargoodboat@yahoo.com wrote... > >> > > >> > This 650V part puts an enhancement-mode GaN FET in cascode with a > >> > depletion-mode GaN JFET. It's real, and it's kind of interesting too: > >> > https://www.transphormusa.com/en/document/650v-cascode-gan-fet-tph3206psb/ > >> > >> LMG3410R070, 600V 40A GaN, 100V/ns, integrated driver and protection. > > > > I have to make accurate fast rectangular pulses with flat tops > > and high edge timing accuracy, so for now I'm wary of having > > that much complexity between my trigger and the output signal. > > There's very little in the signal path. And the 20ns delay to > *the MOSFET output* is about as fast as you'll find. My only > complaint is that the FETs are too big, too much capacitance. > When switching a 50-ohm cable-matching output resistor, a low > 70-milli-ohm Ron is serious overkill. > > > -- > Thanks, > - WinHey Win, here's a smaller-sized version of the same concept, driver-plus-GaN on a chip: <https://media.digikey.com/pdf/Data%20Sheets/Navitas%20Semi%20PDFs/NV6113%20Datasheet%20(FINAL)%208-28-18.pdf> 600V and 300 milliohms instead of 70 milliohms. Cheers, James Arthur
